szehon-ho commented on code in PR #12334: URL: https://github.com/apache/iceberg/pull/12334#discussion_r1978283986
########## format/spec.md: ########## @@ -1754,6 +1754,14 @@ Snapshot summary can include metrics fields to track numeric stats of the snapsh | **`engine-name`** | "spark" | Name of the engine that created the snapshot | | **`engine-version`** | "3.5.4" | Version of the engine that created the snapshot | +### Assignment of Snapshot IDs and `current-snapshot-id` + +Writers should produce positive values for snapshot ids in a manner that minimizes the probability of id collisions and should verify the id does not conflict with existing snapshots. Producing snapshot ids based on timestamps alone is not recommended as it increases the potential for collisions. + +The reference implementation uses a type 4 uuid and XORs the 4 most significant bytes with the 4 least significant bytes then ANDs with the maximum long value to arrive at a pseudo-random snapshot id with a low probability of collision. + +The reference Java implementation writes `-1` for "no current snapshot" with V1 and V2 tables and considers this equivalent to omitted or `null`. This has never been formalized in the spec but for compatibility, other implementations can accept `-1` as `null`. Java will no longer write `-1` and will use `null` for "no current snapshot" for all tables with a version greater than or equal to V3. Review Comment: Should we just put 'The reference Java implementation' in the first pargraph then the first time we mention it? `The reference Java implementation uses a type 4 uuid and XORs the 4 most significant bytes with the 4 least significant bytes then ANDs with the maximum long value to arrive at a pseudo-random snapshot id with a low probability of collision.` And then can use Java threafter (including the second paragraph)? Then its more clear that both paragraph refer to the same one. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For additional commands, e-mail: issues-h...@iceberg.apache.org
